.44 ANATOMY AND PHYSIOLOGY 



visable to add some further explanation relating tr 

 the physiological functions of its respective part 

 besides the incidental notices on this head already 

 given. The food to be transmitted through it 

 various chambers, if of a solid substance, undergoe 

 a process of mastication by the oral instruments ; bu 

 this process is not in all cases equally complete 

 Many predaceous kinds, particularly among the Cole 

 optera, masticate their food very imperfectly, merely 

 dividing it into such pieces as admit of being swal- 

 lowed. Further mastication is doubtless rendered 

 unnecessary in their case by the presence of a 

 gizzard where the trituration is afterwards per- 

 fected. Raptorious species destitute of the organ just 

 named, (such as Dragon-flies) thoroughly comminute 

 their food before swallowing it. Solid vegetable 

 matters are of course always considerably reduced in 

 the mouth ; but those insects which feed on green 

 leaves, particularly the caterpillars of Lepidoptera, 

 swallow the small pieces they detach almost or en- 

 tirely unchanged. In suctorial insects, as well as 

 those which have been termed Lappers (the Stag- 

 beetle is an example), mastication obviously becomes 

 superfluous. 



But it is not the mechanical action of the trophi 

 (as the oral organs are sometimes called) alone that 

 the food is subjected to in the mouth ; it is here that 

 it mingles with the secretions of the salivary vessels. 

 These secretions consist of a whitish, frequently a 

 purely hyaline fluid, said to be of an alkaline nature. 

 The intermixture, to adopt Burmeister's words, has 



